1. Field of the Invention
The present invention relates to a dual data system for duplicating data to prevent the data from being erased and also to make the data highly reliable when the data are written in a storage device.
2. Description of the Related Art
Heretofore, there have been known in the art duplex data systems for duplicating data to be stored by writing the data into two storage devices such as hard disks for data protection in the event of a failure of one of the storage devices. See, for example, JP-A-1981-129964. It is the general practice to write the data simultaneously into the two storage devices.
When one of the storage devices becomes defective and fails to operate, the duplex data system can read the data from the other normal storage device. Therefore, when the power supply of the duplex data system is turned on next time, the duplex data system can be recovered using the data stored in the other normal storage device.
The conventional duplex data system is designed for use in a stationary apparatus such as a server or the like which is continuously supplied with electric energy from an uninterruptible power supply unit or the like. If the duplex data system is incorporated in a cell-powered portable terminal, the duplex data system does not expect abnormal power failures caused by the draining or removal of the cell, operator's erroneous actions, etc. while data are being simultaneously written into two storage devices in the portable terminal.
When the duplex data system suffers an abnormal power failure while data are being simultaneously written into the two storage devices, the two storage devices are turned off abnormally. At this time, the data that are being written into the two storage devices, and other data that have previously been stored in the two storage devices may possibly be destroyed. If both of the two storage devices malfunction due to data destruction or the like, then when the power supply of the duplex data system is turned on, the duplex data system cannot be recovered normally as no normal data can be read from any one of the storage devices.